Background and aims: Familial hypercholesterolemia (FH) is an inherited, metabolic, autosomal dominant disorder. It is characterized by abnormal high total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels. The elevated LDL-C levels are caused by mutations in genes affecting the LDL receptor. The risks of atherosclerosis and premature cardiovascular disease in patients with FH are extremely high due to the poor lipid profile. To date, there is limited experience and knowledge about treatment of FH in children, and which requires further investigation. This thesis aims to identify effects of monitoring of participants involved in previous trials at the Lipid Clinic when they were children. Objective and subjective parameters were both evaluated in order to detect factors of importance regarding the development and handling of the disease. Subjects and methods: This was a systematic clinical exploratory follow-up study, which included both retrospective and present measurements. 67 adults (>18 years), who had previous participated in clinical trials when they were children, were recruited. LDL-C levels were compared in several different groups and subgroups, among other between (1) statin users versus non-statin users, (2) gender, (3) according to outpatient control routines, (4) medication routines and (5) SmartDiet score. We also investigated subjective parameters, among other reasons for poor adherence and not taking cholesterol-lowering medication. Results: 19 out of 67 participants (28%) did not use statins at time of follow-up. Statin users had a significant lower LDL-C level than non-statin users (P <0.001). The reduction in LDL-C level among statin users from time of diagnosis to follow-up were 50%, but only 12.8% of the statin users achieved the treatment goal of LDL-C <2.5 mmol/L. Both genders had a significant reduction in LDL-C and TC levels (P <0.001). Females had a greater reduction in LDL-C levels than males (55% and 23%, respectively). No explanations for the greater reduction in females were found. There was also a significantly lower LDL-C level in participants who had their last outpatient control during the last two years before our follow-up (P = 0.044), and a numerical lower LDL-C level in those who had an outpatient control every two years or more often compared to participants with less frequent outpatient controls (P = 0.069). Conclusion: The great difference in lipid parameters between statin users and non-statin users illustrates the importance of adequate and continuous medical treatment when diagnosed with FH. Further research may be beneficial to explore why females had greater reduction in LDL-C level than males in our follow-up. FH is a chronic disease, and this present study shows the importance of good outpatient control routines in children (<18 years) and young adults.